Metabolic adaptive responses in cancer. Project Summary Oncogenic mutations alter signaling pathways to drive metabolic pathways that meet the bioenergetic and biosynthetic demands of increased tumor cell growth and resistance to cell death. The ribosomal protein S6 kinase 1 (S6K1) supports glycolysis downstream of oncogenic mutations to support growth and survival. Increased glycolysis renders cells addicted to glucose metabolism, and cells are consequently hypersensitive to interruptions in glycolytic metabolism. We recently investigated S6K1 as a target for reducing cellular glycolysis in leukemia cells. Decreased glycolysis upon S6K1 inactivation triggered cell death only cells that were transformed by loss of Pten. Other leukemia cells expressing the BCR-ABL oncogene adapted to decreased glycolysis in the absence of S6K1 signaling, initiating a Metabolic Adaptive Response, or MAR, to mediate cancer cell survival despite S6K1 inactivation. We show here that BCR-ABL cells activate fatty acid oxidation (FAO) in response to loss of S6K1. Treatment of cells with a FAO inhibitor enhanced the cytotoxic responses of BCR-ABL+ cells to S6K1 inactivation or mTORC1 inactivation. Thus, by understanding and targeting the MAR in leukemia cells, we were able to dramatically enhance the potential therapeutic efficacy of inhibitors targeting S6K1 and mTORC1. Experiments in this application are focused on determining the molecular mechanisms and functional impact of the S6K1-regulated MAR. Using metabolomics, we will delineate the precise FAO metabolic pathways that respond to S6K1 activity. In addition, we will test specific signaling mediators downstream of S6K1 BCR-ABL for their role in mediating the MAR. Autophagic metabolism is a MAR program that, along with FAO, is known to prevent cytotoxic responses to mTORC1 inhibitors. We will test here whether targeting S6K1 circumvents autophagic metabolism compared to targeting mTORC1. Finally, we will develop in vivo models of leukemia that will allow us to specifically test the contributions of S6K1-glycolysis and the FAO-MAR on leukemogenesis and therapeutic response. The project combines mechanistic analysis of metabolism and signal transduction with translational analysis of functional impact, and will yield the experimental framework for developing therapies that target S6K1 and the FAO Metabolic Adaptive Response in cancer cells.